rewrite question

Hi,

I'm new to nginx and would like to rewrite some of my dynamic url's to friendly ones. The one particular one I am having trouble with is:

http://www.mysite.com/activities?utf8=%E2%9C%93&q%5Bsport_id_eq_any%5D%5B%5D=&q%5Bsport_id_eq_any%5D%5B%5D=47&q%5Btiming_option_start_time_eq_any%5D%5B%5D=&q%5Barea_id_eq_any%5D%5B%5D=&commit=APPLY

AND
http://www.mysite.com/activities?utf8=%E2%9C%93&q[sport_id_eq_any][]=&q[sport_id_eq_any][]=47&q[timing_option_start_time_eq_any][]=&q[area_id_eq_any][]=&commit=APPLY


for both of the above, I would like to rewrite the url without redirecting to http://www.mysite.com/acitivity/Yoga

Please let me know where is the best place in nginx to perform this change in the config file and what the change would be

thanks in advance.